1. Field of the Invention
The present invention relates to a method and associated apparatus for the production of lithium by direct electrolysis of lithium carbonate and, more specifically, it relates to such a system employing an improved barrier member.
2. Description of the Prior Art
The demand for lithium has increased substantially over the years. It is anticipated that large quantities of the material will be needed for such uses as batteries and aircraft alloys, for example. Both of these uses are expected to require large quantities of pure lithium metal and new techniques for providing the metal will be needed.
It has been known to produce lithium through the electrolysis of lithium-containing fused salts. See generally, U.S. Pat. Nos. 3,560,263; 4,139,428; 4,200,686; 4,405,416; 4,533,442; and 4,617,098.
It has been known to produce metallic lithium on a commercial basis through the electrolysis of lithium chloride which has been produced from lithium carbonate. In the production of lithium chloride from spodumene, the major domestic raw material for the production of lithium, lithium carbonate is an intermediate product. See generally, Mahi et al., Journal of Metals, Vol. 38, No. 11, pp. 20-26 (1986). Among the problems with this approach have been the corrosion of equipment in the recycling of chlorine gas and the relatively high cost of producing lithium chloride from lithium carbonate.
United Kingdom Patent No. 1,024,689 discloses a fused salt electrolysis process for preparing lithium from lithium carbonate. The lithium carbonate is charged to an anode compartment wherein it reacts with gaseous chlorine This produces lithium chloride which is used to produce lithium. See, also, U.S. Pat. No. 3,344,049.
U.S. Pat. No. 4,455,202 discloses a process for producing lithium from lithium-containing compounds including lithium carbonate by electrolysis. The lithium is reduced into a liquid metal cathode to form an alloy. The alloy may subsequently be used to produce lithium.
It has been suggested to produce lithium by direct electrolysis of lithium carbonate through efforts to separate lithium from the carbonate by use of a liquid metal bi-polar electrode. Unfortunately, such efforts did not provide effective means for resisting undesired reactions between the lithium and dissolved lithium carbonate in the cathode to form lithium oxide and elemental carbon.
It has also been known to employ separators in fused salt electrolysis or similar processes. See generally, U.S. Pat. Nos. 590,826; 641,276; 3,248,311; 3,479,274; 3,539,394; 3,645,792; 4,054,678; and 4,680,101.
U.S. Pat. Nos. 590,826 and 641,276 describe diaphragms with little guidance as to specific end uses except for general electrolysis of hydroxides, nitrates or sulfates. There is disclosed a mechanical arrangement wherein packed powder which consists of vitreous oxides is contained between porous screens with the entire assembly acting as a diaphragm.
In spite of these prior art teachings there remains a very real and substantial need for an effective means for the production of lithium by direct electrolysis of lithium carbonate.